Joseph d



(N M a 1. 1 o 0e) J.D.01TE.

, DASH POT.

No. 893,690. Patented Nov. 27, 1888.' F 1g.

R O T N E V m Fig- 1- and without jar and noise.

UNITED STATES PATENT rricE.

JOSEPH D. OrrE, OE EisHKiLL-ON-THE-HUDSON, NEW YORK, AssiGNOE rro THE EIsHKiLL LANDING MACHINE COMPANY.

DASH-POT.

SPECIFICATION forming part of Letters Patent No. 393,690, dated November 27, 1888.

A Application filed February 14,1888. Serial No. 264,028. (No model.)

To all whom it may concern.-

Beit known that I, JosErH D. CITE, who have declared my intention to become a citizen of the United States, and am a resident of Fishkill-on-the-Hudson, Dutchess county, New York, have invented certain new and useful Improvements in Dash-Pots, of which the following is a specification.

,My invention relates to devices for automatically closing the inlet-ports of steam-engines provided with cut-off-valve gear. These devices are commonly called dash-pots. In engines of the class to which my invention will be applied the lever of the steam-inlet valve is liberated automatically by a movement of the parts under the control of the governor, and the valve is theninstantly returned and the port closed by the dash-pot. The sole purpose of the dash-pot is to quickly close the steam-inletwhen the valve is released at the proper point in the stroke; and to be effective it is desirable that it shall do its Work quickly The ordinary vacuum dash-pot comprises a cup-like cylinder or pot and a piston playing therein which is connected to the valve-arm. The extent of lift of the piston in the pot varies directly with the cut-off. I Another form is the weight dashpot, wherein the valve is closed by the descent of a heavy weight, the movement of which varies also directly with the cutoff. The work to be performed by the dash-pot will vary with the pressure of steam in the generator and with the cutoff. This work is due to the friction of the valve on its scat, and will be proportionate to the travel of the valve. The force required to close the valve must then act through a distance proportionate tothe travel of the valve. Thisforceis applied to the valve through the medium of connecting parts,which by their movement acquire a momentum which must be counterbalanced by an exterior force, andl as the momentum increases with an increase in the travel of the valve operated the counterbalancing force should be automatically proportioned to the variable travel of 'the valve.

In both forms of the ordinary dash-pot the momentum acquired by the parts in motion will bring down the weight or piston forcibly and produce a disagreeable hammering and pounding, which must be obviated by an air-cushion; but the forcible escape of this air, necessary to allow the piston or weight to reach the end of its stroke, produces a whistling noise, which is also disagreeable. In neither of these forms of dash-pot is the cushion made to vary automatically with the lift, and if set for a certain lift it must be varied when the point of cut-off is altered.

The object of my invention is to produce a dash-pot. which Will neither pound nor pro- -duce a whistling noise, and one which will adapt itself automatically to all conditions or degrees of cut-off to a sufficient extent.

My invention will be fully described hereinafter, and its novel features carefully defined in the claims.

In the drawings which serve to illustrate my invention, Figure 1 is a side elevation of a vacuum dash-pot embodying my invention. Fig. 2 is an axial section of the same in the plane indicated by line 2 2 in Fig. l, and Fig. 8 is a horizontal section in the plane indicated by line 3 3 in Fig. 2. Fig. 4. is a sectional View similar to Fig. 2, but on a smaller scale, illustrating the application of my invention to a weight dash-pot.

A represents a cylinder closed at the bottom by a base or head, AX. This cylinder is bored out to receive a closetting piston, B. This piston has a stem, BX, of comparatively large diameter, which fits and plays in a bore formed in the reduced neck or upper part, a, of the cylinder.

C is the connecting-rod which couples the piston to the arm of the valve. This rod is or may be connected to the piston-stem by a balland-socket joint in a well-known way. The construction described provides a close chamber, x, of annular form, behind the piston, which I will call, for convenience, the upper vacuum-chamber, and a close chamber, y, in front of the piston, which I will call the lower vacuum-chamber.

On the side of cylinder A is formed a suitable valve-seat, c, on which rests a valve, d, of leather or other like yielding material, which closes two ports, e eX, the former opening into the upper vacuumchamber, rv, at its top, and

the other opening into thclower vacuum-chamber, y, near its bottom. The leather valve d is held lirmly up to its seat by a double leafspring, g, secured to the cylinder at its middle by screws or the like and its free ends resting on the valve over the ports e ex, as shown. In t-he bottom of chamber y is placed a cushion, h, of rubber, leather, or the like; but this l do not consider absolutely essential to the proper working of my invention.

rIhe valves controlling ports c cX are cheekvalves and do not allow any air to enter the vacuum-chambers from without. As the port eX enters chamber y a little way above the bottom of said chamber, it necessarily follows that when piston Bshall have descended far enough to mask this port the air remaining below will serve as a cushion to assist in eounterbalaneing the inertia of the descending parts.

lt will be seen that the displacement in chamber y when the piston B descends will be equal to the displacement of its stem BX plus the displacement in chamber a when said piston rises.

The operation is as follows: Vhen the piston B is first set in motion and rises, air is displaced in vacuum-chamber a: and escapes at port c. The proportion of air displaced will depend on the lift of the piston. A partial vacuum is formed below the piston when it rises. When the valve is released,the piston descends rapidly under atmospheric pressure. In its descent a partial vacuum is formed in chamber a', due to the rarefaction of the air therein. This produces a retarding effect toward the end ofthe pistons descending stroke and overcomes the momentum of the piston, thus obviating the hammering or pounding of the piston commonly heard in these devices.

It will beseen that the work done by my dashpot is directlyproportional to the travel of thc piston, and that the piston is arrested or held back by a force directly proportional to the extent of fall or downward movement of the piston,which rendersits action automatic and adapts it to any degree of eut-off. The whistling noise is wholly obviated, as there is no expulsion of air on the sudden downstroke, and the upstroke is effected so slowly, comparatively, that the small quantity of air expelled in making that stroke will produce no noise. Thus my dash-pot operates without appreciable noise of any kind, the momentum of the parts being overcome by a vacuum, so to speak, instead of by an air-cushion. The small quantity of air incarcerated under the piston at the cud of its downstroke serves as a sort of spring to neutralize the inertia of the parts and start the piston ou its upstroke.

When my invention is applied to a vacuum dashpot,l make the piston hollow, as shown, so as to reduce its weight as much as possible; but when it is applied to a weight dash-pot, as seen in Fig. 4, the piston or plunger will be given the necessary weight to perform its work properly.

The rationale of my dash-pot is this: When the val ve is opened to its fullest extent, the piston will be raised toits highest point. This will displace nearly all the air in chamber w.

When the valve is released,the piston will suddenly descend, and will acquire a maximum momentum, due to the excessive fall; but the vacuum produced behind itin chamber :v will be the more nearly perfect for the same rcason, and will be the more potent as a force to neutralize the momentum. Now suppose the valve only opens to a slight extent and the piston rises only a little; then,when the valve is released and the piston descends, the latter will have very little momentum, owing to the diminished fall. At the same time, owing to the slight displacement produced in chamber a: by the diminished rise of the piston, the vacuum in said chamber produced bythe pistons descent will be very imperfect and have little potency.

' I have here treated vacuum as a positive force merely for convenience. If the vacuum in chamber .fr were perfect, then the atmospheric pressure tending to drive down the piston B would be measured by the area of its stem BX-the minimum. If the chamber a3 were fully open to the atmosphere, then the atmospheric pressure tending to drive down the piston B would be measured by its full area-the maximum.

The difference ofarea of the stem BK and piston B may be fixed approximately to suit the conditions; but the potency of the vacuum in chamber :r may be modified at will by providing said chamber with an air-cock, as i, or some similar device for admitting a small quantity of air thereto. This would be substantially equivalent to effecting a variable enlargement of the area of the stem BK of the piston and a corresponding lesscning of the annular chamber around it.

Of course any known form of cheek-valve might be employed to control the ports c cx. The construction herein shown is simple and efficient. I may say, also, that'it is immaterial to the operation of my dash-pot which of the two elements of the same is the moving part, the cylinder or the piston.

Having thus described my invention, I claiml. A dash-pot containing a piston having differential areas, with a vacuum-chamber on the side of the piston of the lesser area, substantially as set forth.

2. A dash-pot comprising a cylinder with a main bore for the piston and a lesser bore for the pistonstem, a piston in said cylinder havinga stem which fits said lesser bore, and a cheek-valve controlling a port in said cylinder' behind said piston, substantially as set forth.

3. In a dash-pot, the combination of the cylinder,closed at the bottom and provided with two bores of different diameters,` and with ports c cX at its ends for the escape of air, of the piston, which lits the larger bore in said cylinder and has a stern which fits the lesser bore in same, and check-valves controlling the IIO ports in said cylinder, substantially as set over said ports, and the leaf-spring g, resting forth. r v on said valve and secured at its middle to the 4. In a dash-pot, the combination, with the cylinder, substantially as set forth. cylinder A, having a neck, a, and ports e e", In witness whereof I have hereunto signed 15 5 of the piston B, having a stem, BX, the eheckmy name in the presence of two subscribing valves controlling the ports in the cylinder, Witnesses. and an air-cock in said cylinder behind said piston, as set forth.

5. In a dash-pot, the combination, with the Witnesses: ro cylinder A, having a valve-seat, c, and ports ROBERT S. HALPIN,

e eX, of the valve d, of soft material,extending M. E. CURTISS.

JOSEPH D. CITE. 

